Abrasive grain and method for producing it, grinding tool and method for producing it, grindstone for grinding and method for producing it, and grinding apparatus

ABSTRACT

An abrasive grain according to the present invention consists of porous particle material in which a large number of fine particles for cutting blade form gaps partly among them and bond loosely each other. The particles for cutting blade are produced by growing primary particles in secondary particles, which are formed by condensing a large number of primary particles, with heat treatment at a temperature of forming necks at bonding points among the primary particles. Therefore, it is possible to have stable processing for many hours with maintaining excellent quality very effectively.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a grinding tool to carry out finish machining of hard and fragile materials, such as silicon and glass and metal materials, for example, steel and aluminum, a method for producing the tool, an abrasive grain for producing the grinding tool, a grinding apparatus which has the grinding tool, especially to a grinding tool having a long operating life and a method for producing the grinding tool, which contributes to high quality and high efficiency of processing.

[0003] 2. Description of the Prior Art

[0004] For final finishing of parts, which are made of silicon wafer, glass disk, various hard and fragile materials, and metal materials, grinding processing which uses abrasive slurry has been widely used because it is easy to use a fine abrasive grain so that fine finishing surface cannot be obtained easily. Using a large amount of abrasive slurry can also maintain a stable processing characteristic.

[0005] However,this grinding processing, which uses the abrasive slurry, requires a large amount of slurry, and discharges a large amount of slurry waste, so that it has influence on environment.

[0006] This grinding processing has also a limit for improvement of processing efficiency. This is why, development of a fixed abrasive grain processing tool, which can produce an excellent finishing surface more than a grinding finished surface using the abrasive slurry, is actively carried out in various circle.

[0007] For processing of an abrasive grain, it is an advantageous to use a fine abrasive grain in order to produce excellent surface roughness, so that the fine abrasive grain is used for the fixed abrasive processing tool as well.

[0008] However, in order to produce an excellent surface such as a mirror surface, a contact between a bonding material bonding the abrasive grain and a backing and a work piece is caused by using the fixed abrasive grain processing tool in which particle diameter is less than several μm, and also chip of the bonding material and the abrasive grain is accumulated between the abrasives grain, and then clogging of the abrasive grain is caused.

[0009] As a result, processability is decreased, and in a worst case, the processability does not work.

[0010] Moreover, even though a method for controlling the contact between the bonding material of abrasive grain and the work piece is taken, there is a problem for declining processing efficiency because a diameter of abrasive grain is small.

[0011] On the other hand, when a diameter of large particle is selected to use, it is possible to improve processing efficiency, but quality of the surface is deteriorated, and it tends to be difficult to produce the mirror surface.

[0012] In order to solve these problems, the fixed abrasive grain processing tool, which uses condensed powder as the abrasive grain after granulating the fine abrasive grain, is proposed. (References: Japanese Patent Laid-Open Hei7-164324, Hei8-155840, 2000-198073, 2000-237962, 2000-17684, and 2001-129764, Japanese Patent publication Hei9-504235)

[0013] For this fixed abrasive grain processing tool, the excellent surface roughness is produced by action of the fine abrasive grain, and at the same time, improvement of processing efficiency by the condensed abrasive grain can be accomplished.

[0014] However, in order to get further improvement of processing efficiency, using life of the fixed abrasive grain processing tool should be improved because these technologies do not focus on bonding strength among the fine particles comprising the abrasive grain so that requirement of improving the processing efficiency can not be met.

SUMMARY OF THE INVENTION

[0015] An object of the present invention is to solve problems of said prior art. In other words, the object of the present invention is to provide an abrasive grain, which can maintain extremely high processing efficiency for many hours without loosing surface roughness, long operating life of grinding tool and grinding apparatus, which uses the abrasive grain.

[0016] According to a result based on the inventor's repeated careful research about a fixed abrasive grain processing tool, which uses condensed powder of fine abrasive grain as the abrasive grain after granulating the fine abrasive grain related to said prior art, it has been proved that basically, bonding strength among particles comprising the abrasive grain is very important factor although it is influenced by work piece.

[0017] In the prior art, the bonding strength among the particles comprising the condensed abrasive grain has not been noted and studied at all.

[0018] After used the abrasive grain for processing of grinding, the abrasive grain is abraded away gradually and becomes planarized. A flat surface or a surface similar to a flat surface, which is generated by the planarization, is a processing surface.

[0019] High grinding efficiency is achieved when using the abrasive grain consisting of sintered ceramic. However, this abrasive grain is too hard to use because it does not have gaps. As a result, big scratch is newly generated on the surface of the work piece by processing, and then the surface roughness is deteriorated

[0020] On the other hand, when using the abrasive grain consisting of the secondary particles, which is formed by the condensed fine primary particles, high grinding quality is achieved because a sort of cutting blade is formed by the primary particles and the gaps.

[0021] However, this abrasive grain consisting of the secondary particles, which is formed by the condensed fine primary particles, can not be achieved to high grinding efficiency if the primary particles are too fine, or the bond among the primary particles are not controlled. This abrasive grain can also not be achieved to practical use of durability and the operating life.

[0022] At this point, the present inventors found out that for the abrasive grain, which is formed by gathering the fine particles, it is possible for the abrasive grain to be abraded away gradually by controlling the bond strength among the fine particles.

[0023] According to this abrasive grain, new cutting blade is generated consistently, and it is possible to maintain high processing efficiency for the work piece and an excellent processing characteristic, which can produce high quality of surface corresponding to nanometer, for many hours. As the result, the abrasion of the abrasive grain itself is also controlled, and the tool can be used longer.

[0024] In other words, characteristic of the abrasive grain related to the present invention consists of porous particle material. The porous material consists of a large number of fine particles for cutting blade, which form gaps partly, and bond loosely each other. A large number of the fine particles for cutting blade are produced by growing the primary particles in the secondary particles, which are formed by condensing a large number of the primary particles, with heat treatment at a temperature of forming necks at bonding points among the primary particles.

[0025] According to this abrasive grain, when the abrasive grain is actually used, at least one part, which is contacted to the gaps of the particles for cutting blade on the processing surface, acts as the cutting blade. New particles for cutting blade are projected sequentially on the processing surface while the part becoming the cutting blade is lost by abrasion of the particles for cutting blade.

[0026] Consequently, when processing of grinding the cutting blade is always generated voluntarily for the abrasive grain, and it makes easy to eliminate waste of the grinding and maintain the excellent quality effectively. Therefore, it is possible to have stable processing for many hours.

[0027] It is desirable that strength of compression failure for the abrasive grain is more than 1 MPa and less than 500 MPa.

[0028] If the strength of compression failure for the abrasive grain exceeds 500 MPa, the scratch tends to be generated easily so that possibility of lowering the quality of processing surface becomes higher. On the other hand, if the strength of compression failure for the abrasive grain is lower than 1 MPa, there is a possibility that a pre-finished surface of work piece cannot be eliminated completely. Because the bonding strength of the particles for cutting blade is too weak, so that processing of grinding cannot be operated sufficiently, and hard abrasion is caused, then the processing efficiency extremely declines. Moreover, grinding burn tends to be generated easily when it is applied to the grindstone.

[0029] At this point, the grinding burn is generated by the contact between the bond to fix the abrasive grain and a work piece because the grindstone cannot have projection of the abrasive grain. Moreover, if the grinding burn is caused, tarnish of the grinding surface is generated since the processing of grinding is not operated normally, and temperature of the grinding surface goes up.

[0030] According to this, the abrasion of the abrasive grain itself and the degree of fallout, which is generated as loosing the part becoming the cutting blade by the abrasion of the particles for cutting blade, is optimized, so that the fine surface quality can be maintained with processing very effectively.

[0031] At the same time, the abrasion of abrasive grain can be controlled, so it is possible for the abrasive grain to keep a good balance among processing efficiency, processing quality, and longer operating life. Therefore, it is possible for the grinding tool, which has the abrasive grain, to have long operating life.

[0032] It is more desirable that the strength of compression failure for the abrasive grain is more than 20 MPa and less than 300 MPa.

[0033] By using this abrasive grain, high quality of surface can be maintained with processing the work piece very effectively. It is also possible to control the abrasion of abrasive grain effectively, and have longer operating life for the grinding tool.

[0034] It is desirable that pores specific surface area of the abrasive grain is more than 18000 cm²/ cm³ and less than 700000 cm²/ cm³.

[0035] If the pores specific surface area is less than 18000 cm²/ cm³, the scratch of surface tends to be generated easily so that the possibility of deteriorating the quality of surface becomes higher.

[0036] On the other hand, if the pores specific surface area is bigger than 700000 cm²/ cm³, since the bonding strength among the particles for cutting blade is too weak, processing of grinding cannot be operated sufficiently. As a result, it has a possibility that the pre-finished surface of work piece cannot be eliminated completely because hard abrasion of abrasive grain itself is caused, and the processing efficiency extremely declines. Moreover, grinding burn tends to be generated easily when the area is applied to the grindstone.

[0037] According to this, the abrasion of abrasive grain itself and the degree of fallout, which is generated as loosing the part becoming cutting blade by the abrasion of particles for cutting blade, are optimized to maintain the fine surface quality with processing very effectively, and at the same time, the abrasion of abrasive grain can be controlled. Therefore, it is possible for the abrasive grain to keep a good balance among processing efficiency, processing quality, and long operating life. It can make the grinding tool comprising this abrasive grain operates longer.

[0038] It is more desirable that the pores specific surface area is more than 100000 cm²/ cm³ and less than 300000 cm²/ cm³.

[0039] By using this abrasive grain, high quality of surface can be maintained with processing very effectively. At the same time, the grinding tool, which has this abrasive grain, can be operated longer by controlling the abrasion of abrasive grain effectively.

[0040] Moreover, it is desirable that average particle diameter of particles for cutting blade of the abrasive grain should be smaller than 5 μm.

[0041] If the average diameter of particles for cutting blade of the abrasive grain exceeds 5 μm, the scratch is generated on the processing surface, and quality of surface tends to be declined. It is an undesirable situation. In order to fit the average diameter of particles for cutting blade within 5 μm, it is possible to control the heat treatment condition.

[0042] By using this abrasive grain, the excellent quality of surface is definitely produced.

[0043] Moreover, if a binder, which bonds the particles for cutting blade to the abrasive grain, is not used, when the new particles for cutting blade are projected sequentially as loosing the part becoming the cutting blade by the abrasion of particles for cutting blade, insufficiency of projection amount from the binder of the particles for cutting blade can be prevented.

[0044] Problems for the processing quality such as crushing, clogging, residue of the binder, generation of the scratch by attaching the waste of grinding to the binder, and so on can be avoidable.

[0045] This excellent abrasive grain can be produced by means of use of the producing method according to the present invention.

[0046] Consequently, the present invention of producing method for the abrasive grain comprises a process for producing the secondary particles by condensing a large number of the primary particles, and a process for producing the abrasive grain consisting of porous particle material in which the particles for cutting blade is produced by growing the primary particles with the heat treatment at the temperature of forming the necks at the bonding points among the primary particles in the secondary particles, and many of fine particles for cutting blade form the gaps partly and bond loosely each other.

[0047] According to this present invention of producing method for the abrasive grain, when the produced abrasive grain is used actually, the part contacting to the gaps of the particles for cutting blade acts as the cutting blade, and new particles for cutting blade are projected on the processing surface sequentially while the part becoming the cutting blade is lost by abrasion of the particles for cutting blade.

[0048] Therefore, by using the produced abrasive grain, when processing of grinding, the cutting blade is always produced voluntarily for the abrasive grain, and it makes easy to eliminate waste of the grinding and maintain the excellent quality effectively. Moreover it is possible to have stable processing for many hours.

[0049] It is desirable for the heat treatment of this producing method to be operated under the requirement that the average diameter of the particles for cutting blade, which is formed by this method, is smaller than 5 μm.

[0050] If the average diameter of particles for cutting blade exceeds 5 μm the scratch is generated on the processing surface, and the quality of surface tends to be deteriorated. It is the undesirable situation.

[0051] If the grinding tool is produced by use of this abrasive grain, it is possible to maintain excellent quality and have stable and effective processing for many hours by using this abrasive grain, which includes excellent function.

[0052] It is desirable for the grinding tool that the abrasive grain is exposed on a surface of the grinding tool.

[0053] By using this grinding tool, deterioration of processing quality occurred between the abrasive grains or between the abrasive grain and binder, which fixes the abrasive grain and bonds the backing, can be prevented.

[0054] At this point, more than one kind of material from resin, ceramic, and metals can be chosen to use as the binder. Moreover, for example, it is possible to use ceramic precursor to produce ceramic after the heat treatment, and so on.

[0055] The grinding tool can be also selected from grinding film, grinding cloth, and grindstone for the grinding.

[0056] By using the grinding film, the grinding cloth, and the grindstone for grinding, it is possible to bring out effects, which provide high processing efficiency and high quality of processing.

[0057] When the grinding film is produced in accordance with the producing method of this invention, the effects of abrasive grain can be achieved, and at the same time, the grinding film can be produced with low cost. In other words, it is possible for the grinding tool to process grinding with relatively low cost even though the condition of the grinding tool is disposable or similar to disposable.

[0058] When producing the grinding cloth in accordance with this invention, the effects of the abrasive grain can be achieved sufficiently, and at the same time, it is possible to use the grinding cloth instead of using a surface platen for a traditional grinding apparatus and a lapping machine as the grinding tool. Moreover, unlike the grinding film, it is possible for the grinding cloth to be used for many hours since the new abrasive grain is generated on the surface of the grinding tool with the abrasion.

[0059] Therefore, it is possible for the work piece to be finished with the excellent quality of surface effectively. Moreover, the long operating life of this grinding tool contributes to lower the tool cost and reduce task to change the grinding tool for workers.

[0060] Moreover, by adding the abrasive grain of this invention into the grindstone for the grinding it is possible for the work piece to be finished with the stable excellent quality of surface effectively without generating the grinding burn at processing of grinding.

[0061] When producing the grinding film in accordance with the producing method of this invention, it is desirable that a thickness of the binder, which fixes the abrasive grain on a backing film, is smaller than the maximum diameter of the abrasive grain.

[0062] By using this grinding film, the deterioration of grinding quality, which is caused by contact of the binder to the grinding surface, can he prevented, and the amount of projection of the abrasive grain is guaranteed

[0063] It is also desirable that content ratio of the abrasive grain at a part comprising the abrasive grain of the grinding tool is more than 5 percent in volume and less than 90 percent in volume.

[0064] If the content ratio of abrasive is less than 5 percent in volume, it has a possibility that the effect of adding the abrasive grain cannot be received sufficiently. On the other hand, if the content ratio of abrasive grain surpasses 90 percent in volume, strength for maintaining the abrasive grain extremely declines and it cannot be used as the grinding tool because amount of the bonding material for the abrasive grain is too decreased.

[0065] By using this grinding tool, it is possible to have the excellent quality of surface very effectively.

[0066] Moreover, the producing method of the grinding tool for this invention has a process for producing the secondary particles by condensing a large number of the primary particles; a process for producing the abrasive grain consisting of porous particle material in which particles for cutting blade are produced by growing the primary particles with the heat treatment at the temperature of forming the necks at the bonding point among the primary particles in the secondary particles, and many of fine particles for cutting blade form the gaps partly and bond loosely each other; and a process for fixing this abrasive grain to the backing.

[0067] By using the producing method of the grinding tool, it is possible to produce easily the long operating life grinding tool, which can process grinding extremely effective with maintaining the excellent quality.

[0068] Moreover, for the process of fixing the abrasive grain on the backing, it is possible to produce the grinding tool, which satisfies demanded heat resistance, strength and so on, by using more than one kind of binders selected among resin, ceramic, and metal. It is also possible to improve adhesiveness with the binder by a modification treatment for the surface of abrasive grain, which is used for this process.

[0069] Fixing method includes that applying a mixture consisting of such as the binder and the abrasive grain to the backing by using for example wire-bar-coater, gravure-coater, reverse-roll-coater, knife-coater, and so on to the backing.

[0070] Moreover, in the process of fixing the abrasive grain, which is produced by the producing method of this grinding tool to the backing, it is possible to produce the long operating life grinding tool by fixing the abrasive grain on the backing with reinforcing material.

[0071] It is possible to use inorganic fiber such as metal powder, carbon fiber, glass fiber, and so on, organic fiber such as polyacrylonitrile, and so on, and metal fiber, and so on as the reinforcing material.

[0072] When using the fiber, it is possible to use appropriate length of the fiber such as chopped fiber, milled fiber, and so on depending on need. It is also possible to improve the adhesiveness with the binder by the modification treatment for the surface of these fibers. It is also possible to use various type of whisker beside identified above as the reinforcement material.

[0073] Moreover, it is possible to produce the grinding film and the grinding cloth by using the producing method of this grinding tool.

[0074] The producing method of grinding tool related to the present invention has the process for producing the secondary particles by condensing a large number of the primary particles; the process for producing the abrasive grain consisting of the porous particle material in which the particles for cutting blade is produced by growing the primary particles with the heat treatment at the temperature of forming the neck at the bonding points among the primary particles in the secondary particles, and a large number of fine particles for cutting blade form the gaps partly and bond loosely each other; a process for producing an abrasive grain mixture material by mixing or agitating the binder bonding the abrasive grain and the abrasive grain; and a process for producing the grindstone for grinding by forming the abrasive grain mixture material.

[0075] In accordance with the producing method of grindstone for the grinding, the grindstone for the grinding, which can process grinding extremely effective with maintaining the excellent quality, can be produced easily.

[0076] At this point, it is possible to use more than one kind of materials among resin, ceramic, and metal as the binder. Moreover, after using the ceramic precursor, it is possible to produce the ceramic by the heat treatment.

[0077] By using the producing method of the grindstone for the grinding, it is possible to improve rigidity and stiffness by adding the reinforcing materials in the process of producing the abrasive grain mixture material produced by mixing or agitating the bonding material, which bonds the abrasive grain and the abrasive grain. Moreover, the long operating life grindstone for grinding can be produced.

[0078] Moreover, organic fiber, inorganic fiber, and metal fiber is used as the reinforcing material, and it is possible to use the appropriate length of the fiber such as the chopped fiber, milled fiber, and so on depending on need.

[0079] It is also possible to improve the adhesiveness with binder by the modification treatment of surface for these fibers. It is also possible to use various types of whisker as the reinforcing material.

[0080] Moreover, it is possible to improve the adhesiveness with the binder by the modification treatment of surface for these reinforcement materials.

[0081] The grinding tool of the present invention can be attached to the grinding apparatus.

[0082] This grinding apparatus has high processing efficiency, high quality of grinding, and long operating life for the grinding tool, which can reduce the time of changing the grinding tool. It is possible for the grinding tool to have high processing efficiency, high quality of grinding, and long operating life.

BRIEF DESCRIPTION OF THE DRAWINGS

[0083]FIG. 1 is a graph showing a relationship between a load of strength test of compression failure for an abrasive grain and a displacement of pressure.

[0084]FIG. 2 is a photograph of scanning electron microscope (SEM) showing a whole image of second abrasive grain.

[0085]FIG. 3 is a photograph of scanning electron microscope (SEM) showing second abrasive grains, which are enlarged partly before a heat treatment.

[0086]FIG. 4 is a photograph of scanning electron microscope (SEM) showing abrasive grains, which are enlarged partly after a heat treatment.

[0087]FIG. 5 is an enlarged photograph of glass disk surface before grinding of embodiment 1

[0088]FIG. 6 is a chart showing a measurement result of surface roughness for a glass disk surface before a grinding of embodiment 1.

[0089]FIG. 7 is an enlarged photograph of glass disk surface after grinding in embodiment 1.

[0090]FIG. 8 is a chart showing a measurement result of surface roughness of glass disk surface after grinding in embodiment 1.

[0091]FIG. 9 is an enlarged photograph showing a condition of abrasive grains on a surface of grinding film after using as grinding in embodiment 1.

[0092]FIG. 10 is an enlarged photograph of glass disk surface after grinding in comparative example 1.

[0093]FIG. 11 is a chart showing measurement result of surface roughness of glass disk surface after grinding in comparative example 1.

[0094]FIG. 12 is an enlarged photograph of glass disk surface after grinding in comparative example 1.

[0095]FIG. 13 is a chart showing a measurement result of surface roughness of glass disk surface after grinding in comparative example 1.

[0096]FIG. 14 is an enlarged photograph showing a condition of abrasive grains on a surface of grinding film after using as grinding in comparative example 1.

[0097]FIG. 15 is an enlarged photograph of glass disk surface after grinding in comparative example 2.

[0098]FIG. 16 is a chart showing measurement result of surface roughness of glass disk surface after grinding in comparative example 2.

[0099]FIG. 17 is a graph examining a relationship among strength of compression failure for abrasive grain, a surface roughness and a processing efficiency for a grinding film, which comprises various type of strength of compression failure for abrasive grain.

[0100]FIG. 18 is a graph examining a relationship among a pores specific surface area, a surface roughness, and processing efficiency for a grinding film, which comprises various types of strength of compression failure for abrasive grain.

[0101]FIG. 19 is a view showing an example of grinding apparatus for processing silicon installing a grindstone for grinding, which comprises an abrasive grain based on the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0102] An abrasive grain according to the present invention consists of a porous particle material. The porous material consists of a large number of fine particles for cutting blade, which form gaps partly, and bond loosely each other. A large number of the fine particles for cutting blade are produced by growing primary particles in secondary particles with beat treatment at temperature of forming necks at bonding points among the primary particles. The secondary particles are formed by condense of a large number of the primary particles.

[0103] The abrasive grain of the present invention is different from traditional abrasive grain in which the fine primary particles were simply condensed to form the secondly particles. The abrasive grain of the present invention maintains a structure of the porous particle material in which a large number of fine particles for cutting blade form the gaps partly and bonds loosely each other.

[0104] According to the abrasive grain of the present invention, strength of its bonding is stronger compared with strength of its bonding among the primary particles in the traditional grain because the neck is formed at the bonding points of among the particles for cutting blade, which is formed by growing the primary particles with the heat treatment. As a result, it is possible for the abrasive grain of the present invention to use for many hours with maintaining grinding efficiency and grinding quality.

[0105] The particles for cutting blade of the present invention is particles that the primary particles in the secondary particles, which are formed by condensing the primary particles, are grown by the heat treatment, and it is the particles that at least one part of the particles has processing function as the cutting blade for work piece when using it for processing of grinding.

[0106] Moreover, after the heat treatment for growing the primary particles, the primary particles are not only grown by movement of substances, which composes the particles, but also the bonding part of among the particles becomes thicker by movement of the substances, which forms the particles, then becomes a smooth curved surface without discontinuity. That is, after the heat treatment growing the primary particles; it becomes so called “neck”, which is necked as hyperboloid of one sheet (hand drum shape).

[0107] “2.3 Mechanism of Substantial Movement and Model of sinter” in “Technical collection of ceramic material” issued from Industrial Technical Center, Ltd, (issue of S54, April 10, No1) describes in detail about growing the primary particles and forming the “neck” by movement of substance at the heat treatment.

[0108] The abrasive grain of the present invention does not include binder because it is bonded by means of the substances composing the particles for cutting blade among the particles for cutting blade.

[0109] As a result, new particles for cutting blade are sequentially produced on the processing surface as loosing part in which the particles for cutting blade becomes the cutting blade by abrasion.

[0110] Therefore, it is possible to solve a problem that amount of projection from the binder becomes insufficient when forming the abrasive grain by using the binder.

[0111] Moreover, by using the abrasive grain of the present intervention it is possible to solve problems such as occurrence of defects, and so on for the processing quality including crushing, clogging, and generation of scratch by residue of the binder, attachment of waste to the binder, and so on.

[0112] However, when forming the secondly particles by condensing a large number of the primary particles, it is possible to use the binder, which dissolves completely by the heat treatment such as oxygenation, decomposition, evaporation, or the like, and for example the binder consisting of organic material. When using these kinds of binder, it is possible to solve the problem as mentioned above because the binders do not remain when using the abrasive grain.

[0113] The strength of bonding the particles for cutting blade is strengthened by forming of the neck among the particles at the bonding points. As a result, combined with growing the particles itself, it is possible to produce the abrasive grain, which has high processing efficiency rate, high quality of processing, and also long processing hours.

[0114] For materials composing the primary particles of the present invention, it is appropriate to use hard inorganic materials including a characteristic that the substances composing the particles is moved and grown by the heat treatment, and can be adopted as the abrasive grain (can be used as the abrasive grain). These substances include silica, ceria, cubic nitriding boron (cBN), alumina, silicon carbide, zirconium oxide, and so on. It is desirable that the average diameter of particles for the size of primary particles is smaller than 5 μm.

[0115] The secondary particles of the present invention are a coagulation consisting of a large number of fine primary particles. A method for producing these secondly particles by condensing a large number of fine primary particles each other includes a splay drier (Generally, from size of 1_(n)m to 300_(n)m of the secondary particles can be produced. When granulometry is not displayed sharply, classification process is carried out), a sol-gel method, a freeze-dry method, a solvent dry method, and so on, to which the solvent is used together.

[0116] There is another method, which uses thermal decomposition and solid-phase reaction. Moreover, as methods for forming from gas, it is possible to use the methods such as evaporation and coagulation, vapor-phase decomposition, other gas phase reactions, and so on.

[0117] The primary particles in the secondary particles are grown by the heat treatment for the secondary particles, which are produced by these methods.

[0118] The heat treatment of the present invention is conducted under the condition (temperature and time) of growing the primary particles in the secondary particles, which is formed by condensing a large number of fine primary particles.

[0119] The condition of the heat treatment is chosen appropriately by substances, which compose the primary particles. Generally, the temperature is chosen under the condition that the heat treatment can be finished within 10 minutes to several hours. If the time of the heat treatment is too long, it becomes hard to control the particles, and the particles are sintered such as the abrasive grain made of normal ceramic. Even though the particles for cutting blade are not sintered, it becomes the same situation as sintered essentially because the particles for cutting blade become too big. In this case, the effects of the present invention cannot be achieved.

[0120] We have conducted examinations of the heat treatment in advance based on several different temperature and time, and then we have examined structure of inside the particles after the heat treatment by electron microscope and so on, and then we have found out the condition that the bonding part among the particles for cutting blade become the smooth curved surface without the discontinuity.

[0121] In other word, we have found out a condition that the primary particles become the hyperboloid of one sheet as a proof of growing the primary particles, and it is a condition of range, which becomes so called “neck”. It is also the condition of range maintaining the porous materials in which a large number or fine particles for cutting blade form the gaps partly and bond loosely each other.

[0122] These temperature and time are different based on the materials, but in case of the hard inorganic materials as explained above, the temperature is about from 500 to 1600° C., and the time is from several minutes to 24 hours. In this case, it is possible to conduct the heat treatment with pressurizing.

[0123] However, when the particles for cutting blade, which compose the abrasive grain becomes too big by growing, it has the possibility that the effects of the present invention can not be achieved because of off balance. Therefore, it is desirable that the heat treatment is conducted by the condition in which the average particle diameter of particles for cutting blade within smaller than 5 μm of the abrasive grain.

[0124] Moreover, it is preferable to conduct the heat treatment under the condition that the strength of compression failure for producing abrasive grain is more than 1 MPa and less than 500 MPa or the pores specific surface area is more than the 18000 cm²/cm³ and less than 700000 cm²/cm³.

[0125] In accordance with the abrasive grain produced by this condition, it is possible to grind high processing surface quality more effectively together with controlling the abrasion of the abrasive grain.

[0126] It is also possible to use the grinding tool comprising this abrasive grain for longer time. Moreover, it is possible to save time for changing the grinding tool, and also lower the cost, which is required to change the grinding tool.

Testing Example

[0127] Concrete testing examples about the abrasive grain of the present invention is explained as follows.

[0128] However, the present invention is not only limited for these testing examples, it is possible to implement in various way within the range in which the testing example does not deviate from the essential feature of the present invention.

[0129] Moreover the average particle diameter is measured by dry system using Laser Diffraction made of Horiba, Ltd. and Scattering Granulometry Measuring Device LA-920, and the particle diameter of the abrasive grain at 50 percent of frequency accumulation is decided as the average particle diameter (normally called median diameter).

[0130] A test for the strength of compression failure is also carried out by Micro Compression Testing Machine, MCTM500PC made of Shimdzu Corporation based on the report of Hiramatu, Oka, and Kiyama (Japan Mining Industry Magazine 81,1024(1956)).

[0131] Measuring granulation is compressed by using a flat indentator under the test conditions of the test load from 10 to 1000 mN, load speed 0.446 mN/sec, and then the strength in which the granulation is destroyed by compression was measured. FIG. 1 shows relationship between compression displacement at this point and the load as a model at this point.

[0132] The strength of compression failure, T reads the load value at the curved line bending part Q inside the dotted line circle, and then calculated by this value.

[0133] On the other hand evaluation of the surface roughness for the processing surface was conducted by using Form Talysurf S4C made of Taylor-Hobson Ltd.

[0134] Moreover, the fine pores specific surface area of the present invention is multiplied value of BET specific surface, which was measured by absorption and de-sorption of BET one point method for relative pressure 0.3 of nitrogen gas and density of material composing the abrasive grain.

Testing Example 1

[0135] Slurry was produced by adding water (water system binder for example mixture of polyvinyl alcohol water is available to use) into ultra fine zirconium oxide (ZrO₂) powder as the primary particles consisting of the particle diameter from 50 nm to 60 nm. After the spraying the slurry by the spray dryer, secondary particles α, which have 50 μm of the average particle diameter, is produced. The strength of compression failure for these secondary particles α was 0.47 MPa. FIG. 2 and FIG. 3 shows whole scanning electro microscope (SEM) photograph of the secondary particles and partly enlarged the scanning electro microscope (SEM) photograph.

[0136] The heat treatment for these secondary particles α was conducted by use of an electronic furnace. The polyvinyl alcohol, which was used as the binder when forming the secondary particles, is eliminated completely by this heat treatment.

[0137] In accordance with previously examined condition, the temperature of the heat treatment and the time of the heat treatment were adjusted to become the inside particles within the porous particle material, which works as the particles for cutting blade when using as the abrasive grain smaller than 5 μm.

[0138]FIG. 4 shows a partly enlarged SEM photograph (the same magnification as FIG. 3) about an example of the porous particle material (abrasive grain β) consisting of this zirconium oxide in which the heat treatment was conducted by appropriate condition.

[0139] According to FIG. 4, the porous particle material (abrasive grain β), which works as the particles for cutting blade when using it as the abrasive grain, is obviously growing bigger than the primary particles shown in the FIG. 3, and the bond among the particles become the necked hyperboloid of one sheet so called “neck”.

[0140] It is also possible to identify that a large number of fine particles for cutting blade form the gaps partly, and bond loosely each other. Moreover, when the heat treatment is conducted, if the time of the heat treatment is too long or the temperature of the heat treatment is too high, the primary particles are completely sintered, and then become almost absolute sintered compact.

[0141] The abrasive grain β related to the present invention, which was produced by the strength of compression failure 92.6 MP and the average particle diameter 50 μm, is mixed with liquid urethane resin to become the volume ratio of the particles is 35 percent of its volume.

[0142] Moreover, a mixture was produced by mixture and agitation of the particles and resin for ten minutes with an agitator after adjusting solution viscosity by adding methyl ethyl-ketone as the solvent. The agitation was conducted by room temperature and 50 rpm of its revolution speed in which the speed does not destroy the abrasive grain.

[0143] The mixture was applied on the backing (PET film of about 75_(n) m thickness) by using the wire bar coater. Thereafter, it was dried for one hour in a constant temperature tank, which keeps the temperature of 60° C., and then grinding film A as the grinding tool was produced.

[0144] Maximum thickness of produced application layer (a part of comprising the abrasive grain) becomes almost same as maximum diameter of the abrasive grain related to the present invention having the granulometry (By using the solvent, it becomes easier to thin the thickness of the binder's layer).

[0145] The grinding film A produced by this method was attached to a lap platen, then after processing (processing condition: 60 rpm of platen revolution speed, 46 kPa of processing pressure) 30 mm diameter of optics glass disk (borosilicate crown glass (suitable for BK7)), which was adjusted the maximum high roughness Ry becomes 2 μm, mirror surface without scratch in which the maximum height for roughness Ry is less than 30 nm (nanometer) was produced in two minutes.

[0146] After that processing 20 sheets of the same glass disks under the same condition were processed continuously, the processing efficiency and the processing surface roughness were barely deteriorated. At this point, FIG. 5 shows enlarged surface photograph GD of the glass disk before the processing. FIG. 6 shows measurement result (chart) for the surface roughness of the glass disk. Moreover, FIG. 7 shows enlarged surface photograph GD′ (the same magnification as FIG. 5) after processing, and FIG. 8 shows measurement result for the surface roughness.

[0147] It is possible to see that irregularity, which was remained before the processing, was almost eliminated after the processing, and it becomes the mirror surface. Condition of abrasion of the abrasive grain on the grinding film A after processing 10 sheets of glass disks was examined. FIG. 9 shows the condition of the surface A′.

[0148] According to FIG. 9, it is possible to see that the abrasive grain does not have big damage and fallout from the backing by progressing the abrasion gradually along with progress of the processing because the bonding strength among the particles for cutting blade are appropriate.

Comparative Example 1 and 2

[0149] Abrasive grain γ and δ of comparative examples 1, 2 were produced by the same method, which produced the abrasive grain β by using the secondary particles α of the testing example 1. But the heat treatment condition was changed.

[0150] The strength of compression failure for the abrasive grain γ was 0.6 MPa, and the pores specific surface area was 100000 cm²/cm³. The strength of compression failure of the abrasive grain δ 613 MPa, and the pores specific surface area was 3000 cm²/cm³. The average particle diameter of these abrasive grain γ, 67 was 50 μm for the both abrasive grains,

[0151] Examination of each abrasive grain γ, δ, which was conducted by the scanning electron microscope, did not show formation of “neck” at 0.6 MPa of the strength of compression failure of the abrasive grain δ. In other words, it was found that the enough heat treatment was not conducted, so that the primary particles were not growing.

[0152] On the other hand, 613 MPa of the strength of compression failure for abrasive grain δ did not have the structure that a large number of fine particles for cutting edge form the gaps partly and bonds loosely each other and it became almost absolute sintered compact.

[0153] Grinding film B (the strength of compression failure of abrasive grain γ: 0.6 MPa, comparative example 1) and grinding film C (the strength of compression failure strength of abrasive grain δ: 613 MPa, comparative example 2) was produced under the same method as producing grinding film A by using each of these two abrasive grains γ, δ.

[0154] These grinding films B, C were attached to the lap platens respectively, and then processed BK7 optics glass disk which was adjusted the maximum height for surface roughness Ry becomes 2 μm under the same processing condition. For grinding film B, the processing was conducted for 20 minutes, but the maximum height for surface roughness Ry only achieved to 1.275 μm

[0155] When conducting the same processing test by using the grinding film produced by using the second abrasive grain α (strength of compression failure of 0.47 MPa) in which the heat treatment was not done, the processing efficiency was lower than the result of grinding film B, and the processing surface before grinding could not be improved.

[0156]FIG. 10 shows enlarged photograph GD1 of the surface of the glass disk before processing. FIG. 11 shows the measurement result of its surface roughness. Moreover, FIG. 12 shows enlarged photograph GD1′ (expansion magnification is same as FIG. 10) of the surface after 20 minutes processing, and FIG. 13 shows the measurement result of its surface roughness.

[0157]FIG. 14 shows condition of the abrasive grain on grinding film B′ after using as processing.

[0158] These results show that even though the surface roughness of glass disk was improved a little by grinding for 20 minutes using the grinding film B, but the pre-finished surface of glass disk was not removed completely because the hard abrasion of abrasive grain is generated (Reference of FIG. 14).

[0159] On the other hand, when using grinding film C, big scratch was generated newly by processing the surface of the glass disk surface because of using the abrasive grain, which became absolute sintered compact bonding completely among the primary particles. In other words, the maximum height for surface roughness Ry was rather deteriorated as 2.7228 μm (Scratch SK can be seen in the surface expanded picture of FIG. 15).

[0160] Appearance of scratch SK is recognized from the measurement result of the surface roughness (FIG. 16) on the processing surface after grinding. On the other hand, the abrasive grain was hardly abraded away, and the planarization of the edge for the abrasive grain was not seen by observation of microscope.

[0161] Grinding films comprising the abrasive grains, which have several kinds of the strength of compression failure, are produced in the same way. FIG. 17 shows a result of relationship among the strength of compression failure, the surface roughness (sign: □), and the processing efficiency (sign: ⋄).

[0162] In FIG. 17, a vertical axis of processing efficiency shows amount of grinding per hour relatively, and the processing efficiency becomes higher as reaching upper part over the middle part of the graph.

[0163] According to FIG. 17, it is shown that if the strength of compression failure is too small (the strength of compression failure: less than 1 MPa), in other words, if the bonding strength of the particles for cutting blade is too weak, the surface roughness can not be improved much because the processing efficiency is low, and destruction of the abrasive grain is proceeded by processing pressure, so that the processing surface before the grinding can not be eliminated completely.

[0164] Meanwhile, if the strength of compression failure is too strong, for example, in case of almost absolute sintered compact (the strength of compression failure: 613 MPa), the processing efficiency becomes extremely high. However, on the other hand, quality of processing surface is highly deteriorated. In this way, only the abrasive grain related to the present invention, which comprises appropriate bonding strength of the particles for cutting blade, could achieve high quality of processing surface (mirror surface) very effectively. At that time, it was found that the abrasion of the abrasive grain is controlled, and the grinding tool can operate longer.

[0165] About the abrasive grains comprising the various strength of compression failure for the abrasive grain shown in FIG. 17, FIG. 18 shows a relationship between the fine pores specific surface area, which is a parameter showing inside structure of the abrasive grain, and processing efficiency. At this time, the fine pores specific surface area is different from normal specific surface area (unit is ┌cm²/g┘ or ┌m²/g┘ and so on). In other words, the fine pores specific surface area is a parameter, which shows difference of inside structure prominently, because the fine pores specific surface area excludes affect based on difference of specific gravity of material.

[0166] In FIG. 18, processing efficiency of vertical axis shows amount of grinding per hour relatively, and the processing efficiency goes higher as reaching upper part over middle part of the graph.

[0167] According to FIG. 18, it is shown that if the fine pores specific surface area is too big (the pores specific surface area: over 700000 cm²/cm³), in other word, if the bonding strength among the particles for cutting blade is too weak, the processing efficiency is lowered.

[0168] The surface roughness cannot be improved much also because destruction of the abrasive grain by the processing pressure is progressed and the pre-finished processing surface is not removed completely.

[0169] Meanwhile, if the fine pores specific surface area is too small, the structure that a large number of fine particles for cutting blade form the gaps partly, and bond loosely each other, is lost.

[0170] For example, when using almost absolute sintered compact (the pores specific surface area: less than 5000 cm²/cm³), the processing efficiency is extremely improved. However, on the other hand, when using the almost absolute sintered compact, the quality of processing surface is highly deteriorated.

[0171] In this way, the only abrasive grain related to the present invention, which comprises the bonding strength among the particles for cutting blade and the specific structure, could achieve high quality of processing surface (mirror surface) very effectively. At this point, it was found that abrasion of the abrasive grain is controlled, and the grinding tool can operate longer.

Testing Example 2

[0172] Silica abrasive grain, which consists of colloidal silica and diameter of the primary particle (average particle diameter of 50 nm) is condensed to become the average particle diameter is 30 μm by the sol-gel method. Then produced silica powder is dried and secondary particles ε was produced by eliminating water and organic solvent, which are composed in the fine pores.

[0173] For the produced secondary particles ε, which was produced by this method, observation of the scanning electron microscope was conducted after conducted the heat treatment under various kinds of condition.

[0174] From these particles, the abrasive grain ζ related to the present invention is produced. This abrasive grain ζ is the porous particle material in which a large number of fine particles for cutting blade form the gaps partly and bond loosely each other, and also the particles for cutting blade are formed by growing the primary particles with heat treatment.

[0175] The compression failure strength of this abrasive ζ was 124.2 MPa, and size of the particles for cutting blade 1.2 μm.

[0176] Polyurethane resin paint was mixed with produced abrasive grain ζ in which the volume ratio becomes 35 percent of its volume and copper powder of the average particles diameter of 3 mm. After that, the mixture was produced by mixture and agitation of particles and resin for 15 minutes by the agitator at the rotation speed of 60 rpm.

[0177] At this point, it is possible to add blowing agent to form independent bubble depending on need.

[0178] The mixture was poured into circular form metal mold (450 mm_(n)), then it was hardened with the heat treatment at 120° C. for 10 hours, and then the grinding cloth was produced. Produced grinding cloth was attached to the surface platen after cutting it into specified size, and then grinding processing was conducted for silicon wafer of 30_(n)m diameter which was grinded by grindstone of about #2000 in advance.

[0179] As a result, mirror surface, which does not have any scratch and lower than 20 nm of the maximum height for surface roughness Ry, was produced in 10 minutes of processing. Even though grinding of 20 sheets of silicon wafer were conducted continuously; processing efficiency and processing surface roughness were not deteriorated.

[0180] At this point, FIG. 19 shows example of attaching the grinding cloth, which is related to the present invention used for the testing example 2, to grinding apparatus for processing silicon as a model.

[0181] For the FIG. 19, the sign 1 is a work piece, silicon wafer. The silicon wafer is mounted on a rotation part 10. The silicon wafer is rotated by rotation of this rotation part 10. An undersurface of the silicon wafer is also grinded by contacting to the grinding film 2 related to the present invention, which was mounted on a platen 20 (grinding film can be mounted instead of the grinding cloth) in accordance with upward and downward movement of the rotation part 10. Moreover, whole undersurface of the silicon wafer 1 is grinded equally because the surface platen 20 rotates.

Testing Example 3

[0182] Using silica abrasive grain as the grinding cloth was considered. The strength of compression failure of the silica abrasive grain was 18.5 MPa and size of particles for cutting blade was 0.2 μm, which was produced by the heat treatment under different condition from testing example 2 for secondly particles _(n).

[0183] Grinding cloth was produced by use of the silica abrasive grain under the same condition as testing example 2, and processing test of silicon wafer by using the grinding cloth was conducted as well. As a result, mirror surface, which has lower than 20 nm of maximum height for surface roughness Ry, was produced in 15 minutes of processing time. However, after the processing was conducted continuously, the processing efficiency was declined gradually. When processing 5 sheets of the silicon wafer, 30 percent of processing efficiency was declined compared to the beginning of the processing, although the processing surface roughness is the same level, and then it became impossible to process after 15^(th) sheets of the silicon wafer.

Testing Example 4

[0184] Phenol aldehyde resin was mixed with the abrasive grain related to the present invention comprising the average particle diameter of 30 μm and the strength of compression failure of 124.2 MPa as same as used in the testing example 2 in which the volume ratio becomes 45 percent of its volume at last and nickel powder (reinforcement material) of the average particle diameter of 3 μm becomes 15 percent of its volume. After that, the mixture was produced by mixture and agitation the powder and resin for 15 minutes by the agitator at the rotation speed of 60 rpm.

[0185] The mixture was poured into the metal mold, and then grindstone for grinding was produced by hardening treatment for about 5 hours at the temperature of 150° C. with pressuring.

[0186] After the produced grindstone for grinding was attached to vertical axis of Infeed Grinding Machine, and grinded a lapping finished silicon wafer, mirror surface, which has lower than 30 nm of the maximum height for surface roughness Ry, was produced in one minutes of processing time. After grinding for 20 sheets of silicon wafer continuously, grinding burn was not generated, and deterioration of grinding efficiency and surface roughness were not identified.

Testing Example 5

[0187] Grinding processing test for silicon wafer was conducted under the condition, which used the abrasive grain related to the present invention comprising the same strength for compression failure 18.5 MPa as used in the testing example 3, and beside that it was used the same conditions as the testing example 4 to manufacture the grindstone for grinding.

[0188] As a result, a mirror surface, which has lower than 30 nm of maximum height for surface Ry, was produced in one minute of processing time. However, after processing was conducted continuously, grinding burn was generated on the surface of silicon wafer when 10^(th) sheets of silicon wafer were processed.

[0189] As explaining above, the abrasive grain of the present invention consists of the porous particle material. The porous material is composed of a large number of fine particles for cutting blade, which form the gaps partly and combine loosely each other. The particles for cutting blade are produced by growing the primary particles in the secondary particles, which were formed by condensing a large number of the primary particles, with the heat treatment at the temperature of forming the necks at the bonding point among the primary particles. Therefore, when using as the abrasive grain, at least the part, which is contacted to the gap of the particles for cutting blade on the processing surface, woks as the cutting blade.

[0190] The particles for cutting blade are also projected newly on the processing surface sequentially while the part becoming the particles for cutting blade is lost by the abrasion of the particles for cutting blade. Moreover, the bonding strength among the particles for cutting blade is optimized, so that it is possible to maintain excellent quality and have stable processing for many hours very effectively.

[0191] The grinding tool of the present invention also has high processing efficiency, high quality of processing, and long operating life.

[0192] The grinding apparatus of the present invention also has high grinding efficiency, high quality of grinding, and long operating life for the grinding tool.

[0193] According to the producing method of the abrasive grain of the present invention, when processing of grinding, the cutting blade is always generated voluntarily for the abrasive grain. Therefore, it makes easy to eliminate the waste of the grinding, and it is certainly possible to produce the abrasive grain, which can grind very effectively with maintaining excellent quality, stably with high productivity.

[0194] According to the producing method of grinding tool of the present invention, it is also possible to produce the long operating life grinding tool, which can grind very effectively with maintaining excellent quality.

[0195] According to the producing method of grindstone for grinding of the present invention, it is possible to produce the grindstone for grinding, which can grind very effectively with maintaining excellent quality. 

What is claimed is:
 1. An abrasive grain comprising: a porous particle material in which a large number of fine particles for cutting blade form gaps partly among them and are bonded loosely each other, said particles for cutting blade being produced by growing a large number of primary particles in secondary particles with heat treatment at a temperature of forming necks at bonding point between said primary particles, and said secondary particles being formed by condensing said large number of primary particles.
 2. An abrasive grain according to claim 1, wherein when using as an abrasive grain, at least a part contacting with gaps of said particles for cutting blade on a processing surface, acts as a cutting blade, and wherein new particles for cutting blade are projected sequentially on processing surface while a part becoming the cutting blade is lost by abrasion of the particles for cutting blade.
 3. An abrasive grain according to claim 1 or 2, wherein strength of compression failure of the abrasive grain is more than 1 MPa and less than 500 MPa, and wherein the strength of compression failure is more than 20 MPa and less than 300 MPa.
 4. An abrasive grain according to claim 1 or 2, wherein pores specific surface area is more than 18000 cm²/cm³ and less than 700000 cm²/cm³, and wherein the pores specific surface area is more than 100000 cm²/cm³ and less than 300000 cm²/cm³
 5. An abrasive grain according to any one of claims 1 to 4, wherein average particle diameter of said particles for cutting blade is smaller than 5 μm.
 6. An abrasive grain according to any one of claims 1 to 5, wherein a binder is not included to bond the particles for cutting blade.
 7. A method for producing an abrasive grain comprising; a process for producing secondary particles by condensing a large number of primary particles, and a process for producing the abrasive grain consisting of porous particle material in which the particles for cutting blade is produced by growing the primary particles with the heat treatment at the temperature of forming the necks at the bonding points among the primary particles in the secondary particles, and a many of fine particles for cutting blade form the gaps partly among them and are bonded loosely each other.
 8. A method for producing an abrasive grain according to claim 7, wherein average diameter of formed particles for cutting blade is smaller than 5 μm.
 9. A grinding tool comprising an abrasive grain according to any one of said claims 1 to 5 on a grinding surface.
 10. A grinding tool according to claim 9, wherein the abrasive grain is projected on a surface of said grinding surface, and a grinding tool consists of a grinding film, a grinding cloth, and a grindstone for grinding.
 11. A grinding film according to claim 10, wherein thickness of a binder layer to fix said abrasive grain on a backing film is smaller the than maximum diameter of the abrasive grain.
 12. A grinding tool according to any one of claims 9 to 11, wherein content ratio of said abrasive grain at a part including the abrasive grain is more than 5 percent in volume and less than 90 percent in volume.
 13. A method for producing a grinding tool comprising; a process for producing secondary particles by condensing a large number of primary particles, a process for producing an abrasive grain consisting of a porous particle material in which particles for cutting blade are produced by growing the primary particles with heat treatment at a temperature of forming necks at bonding points among the primary particles in the secondary particles, and a large number of fine particles for cutting blade form gaps partly among them and are bonded loosely each other, and a process for fixing the abrasive grain on a backing.
 14. A method for producing a grinding tool according to claim 13, wherein at the process for fixing said abrasive grain on the backing, one or more kind of binders from selected from resin, ceramic, and metal are used.
 15. A method for producing a grinding tool according to claim 13 or 14, wherein in the process for fixing said abrasive grain on the backing, the abrasive grain is fixed on said backing through a reinforcement material.
 16. A method for producing a grinding tool according to claim 15, wherein one or more kind of said reinforcement material are selected and used from metallic powder, organic fiber, inorganic fiber, and metallic fiber.
 17. A method for producing a grinding tool according to any one of claims 13 to 16, wherein said grinding tool is a grinding film or a grinding cloth.
 18. A method for producing a grindstone for grinding comprising; a process for producing secondary particles by condensing a large number of primary particles, a process for producing the abrasive grain consisting of the porous particle material in which particles for cutting blade are produced by growing the primary particles with heat treatment at a temperature of forming necks at boning points among the primary particles in the secondary particles, and a large number of fine particles for cutting blade form gaps partly among them and are bonded loosely each other, a process for producing an abrasive mixture material by mixing or agitating between binder bonding the abrasive grain and the abrasive grain, and a process for producing a grindstone for grinding by forming the abrasive mixture material.
 19. A method for producing the grindstone for grinding according to claim 18, wherein a reinforcement material is added in the process for producing the abrasive mixture material by mixing or agitating said abrasive grain and a bonding material bonding the abrasive grain.
 20. A method for producing a grindstone for grinding according to claim 19, wherein one or more of said reinforcement material are selected and used from metallic powder, organic fiber, inorganic fiber, and metallic fiber.
 21. A grinding apparatus comprising a grinding tool according to any one of claims 9 to
 12. 